Felted-cellulose-fiber product



G. L. SCHWARTZ FELTED CELLULOSE FIBER PRODUCT Filed Sept. 22, 1928 Feb.3, 1931.

. Patented Feb. 3, 1931 UNITED STATES PATENT OFFICE GEORGE L. SCHWARTZOF WILMINGTON, DELAWARE, ASSIGNOB TO E. I. DU PON'I DE NEMOURS &COMPANY, OF WILMINGTON, DELAWARE; A CORPORATION OF DELA'L WAREFELTED-CELLULOSE-FIBER PRODUCT Application filed September 22, 1928.Serial No. 307,760.

, This invention relates to the art of cellulose products and moreparticularly to the art of felted cellulosefiber products.

Many attempts have been made to produce cellulose fiber products bycompacting" the fibers into a felt but the results achieved by previousprocesses have been subject to various objections. In the priorprocesses it has been customary to use binding materials to unite thefibers but this is objectionable because it gives a product of lowporosity, On the other hand, when a binding material has not been usedin the previous processes, the resulting felt has been inherently weak.Also, the products resulting from previous processes have often beenstiff and horn-like, because the gelatinizing action of the substancesused for treating the fibers, such as aqueous solutions of' caustic sodaor zinc chloride, has not been stopped by heat.

It is an object of the present invention to produce felted cellulosefiber products without the use of auxiliary binding materials.

It is another object of the present invention to produce cellulose fiberproducts havinga high degree of pliability. I i

It is a further object of the present invention to so produce. theseproducts that they shall have a greatly increased wet strength.

It is a still further object of the present invention to produce suchproducts having an increased dry strength without being susceptible tothe customary paper break.

It is a still further object of the present invention to produceeellulose fiber products having increased wetfanddry strength withoutimpairing their wetting properties or reducing their porosity. With theabove and other objects in view,

-ceeds, '1 have set forth my invention in'the following specificationand illustrated it in the accompanying drawing, in which:

Fig. is a-diagrammatic side'elevation of an diipparatus for carrying outmy invention, an

Fig. 2 is a diagrammatic planview thereof.

In the accompanyin drawing 10 designates a continuous roll of eltcomposed of fibersso that amended and kinked and which has which will beapparent as the description promounted in any convenient manner,as bysusthereby beenmade in any desired manner. This may be"accomplished,'for example, as set forth in the copendin application ofMcCormick and Schwartz, erial No. 283,445, filed June 6, 1928, theprocess consisting, briefly, in treating cellulose fibers with asolution of caustic alkali for example 8 to 35% sodium hydroxide, attemperatures from slightly below 5 C. to C. This pulp can then beconverted into a continuous roll of felt by any standard papermachinery, such as a Fourdrinier machine.

The roll of felt 10, mounted in any desired manner, passes over a guideroll 11 and is fed on to a wire screen conveyor 12, which may be made ofany suitable material, such as Monel metal, and is supported by guiderolls 13, 14, 15, 16 and 17, and a drum which willbe describedhereinafter.

The conveyor 12 propels the felt 10 forwardly into a bath of coldcaustic solution 18, which is kept in circulation through an overflowconnection 19 between a main caustic tank 20 and an overflow tank 21,and by providing the latter with a gravity outflow pipe 22 at a pointslightly above its bottom. From I thispipe the solution flows into apump 23, driven by any suitable means, which forces the solution up to asupply tank 24, from which it flows by gravity back to the tank so 20.The supply tank 24 may be cooled by any well known means, such as brineor electric refrigeration (not shown).-

Immersion of the felt 10 in the caustic solution 18 is effected by thepassage of the conveyor 12 and the felt 10 over guide roll 14 and undera second guide roll 31, both of which are adjustable to vary the periodof immersion of the. -felt. Guide roll .14 is pending it from a crossbar (not shown), which is carried in a parallel take-up mecha nism33-that has adjusting screws 34 for varying its horizontal distance fromguide roll 31 I, I

efi'ecting an earlier or later im- 'mersion of the felt. Guide roll 31is mounted in bearings 35, which are adjustable vertically byhand-wheels 36 to vary the depth to which the felt is immersed intank20. Guide rolls 16 and 17 are provided with adjusting hand- 1 thelatter being submerged caust c bath 62 contained in a "SOllltIOIl 1s ofrelatively high concentration wheels 37 and 38, respectively, for takingup or providing slack in the conveyor 12 as guide roll 31 is raised orlowered.

This immersion causes the felt to become impregnated with the causticsolution so that its fibers are swollen and their surfaces are sli htlygelatinized.

he impregnated felt 10, supported on the conveyor 12, is passed betweenguide roll 15 and a second guide roll 39, the latter being adjustablymounted with respect to the former. to permit the variation of the spacebetweenthem by hand-wheels 40 and the exertion of any desired intensepressure. These rolls squeeze the excess caustic solution from the felt10, and form it into a rubber-like but very weak sheet, the expelledcaustic flowing back into tank 20.

A second wire screen conveyor 41, supported by a series of guide rolls42, 43, 44, 45, and 46, mounted in a framework 47, and provided withtightening adjustments 48: and conveyor aligning adjustments 48', ismounted above the path of travel of the conveyor 12 and felt 10 to exerta predetermined and regulable' pressure on the upper surface of thefelt'to remove excess caustic solution.

The felt 10 supported on the conveyor 12,

passes over a drum 49 that is perforated at 50 and heated by any desiredmeans, such as steam supplied to a series of spray pipes 51. A suctionhood 52 is preferably mounted on the framework 47 to remove theuncondensed steam, As the felt 10 and conveyor 12 reach thecircumference of the drum 49, conveyor 41 is brought into contact withfelt 10 and steam is injected through the latter, thus stopping thegelatinizing action of the cold caustic solution and, with the aid ofthe pressure applied by the upper screen,

' molding the fibers into a compact felt 53, in

situ. 1

As the felt 53 leaves the drum 49 .it also leaves the conveyors 12 and41 and is received on a third wire screen conveyor 54, supported by aseries of guide 'rolls 55, 56, 57, and 58, as well as by certain pressrolls which will be described hereinafter.

Conveyor 54 carries the felt 53 over guide rolls 55 and 56 and under aguide roll 61, in an aqueous tank 63. This and is maintained at-a hightemperature in any suitable manner, as by gas or oil burners 64. Thistreatment reduces the swelling of fthefibers and causes, them to acquiremore .definite'kinks and curls, accompanied by some shrinkage the areaof the felt.

The latteris now very strong and requires only-com lete washing to freeit from caustic,.-andor this purpose it passes through a .seriesofrubbercovered press rolls which I are independentlyadjustable at'.66 to exert.anydesiredpressure and squeeze out the exmamas frame (not shown), andis wound up on a roll (not shown) or fed to other apparatus (not shown)which fits it for the speclal uses to which it is to be applied.

'The apparatus is driven by any suitable mechanism, such as a sprocketchain 72 which engages a sprocket wheel 73 on the axis of drum 49 and aseries of sprocket Wheels 74 on the driving shafts of the press rolls65. These sprocket wheels are of any desired size, and power istransmitted to sprocket wheel 7 3y from any suitable source (not shown).The power thus transmitted to the drum 49 is sufficient to create afriction drive for the various wire screen conveyors and to feed theuntreated felt 10 forwardly into contact with conveyor 12. I have foundit desirable to provide scraper knives 75, 76, and 77 in the vicinity ofroll 31, roll 39, and drum 49, respectively, to overcome any tendency ofthe felt to follow the contour of these rotary members.

I have also found it desirable to provide the roll 31 with a series ofstaggered slots 78 and to cover it with a Monel metal screen 79 to breakthe vacuum which tends to form between it and the gelatinized fibers,although any equivalent means might be used.

Although the apparatus described herein is one I have found satisfactoryfor carrying and pass it into a 10-11% aqueous sodium. hydroxidesolution at --5 C. for a 5-second treatment, and for the second caustictreatment 1 use an 18% sodium hydroxide solution at 100 to 104 C. for 5seconds or longer.

If a sheet of unsized kraft, made from fibers that have not been curledand kinked, is used as the raw material a considerably lon er time isrequired for impregnation wit the cold caustic solution.

If the starting material is a sheet made from 5-hour cooked cottonlinters it should remain in the cold caustic solution 6 seconds,whereas-if the sheet is made from 20-hour cooked linters this time maybe reduced to 3 seconds.

.To'produce a relatively stilt felt the time of impregnation in the coldcaustic bath is increased, but if a relatively pliable felt is teria'lused and i ficial fibers,

desired the time of impregnation is decreased.

' Consequently, according to the raw mathe degree of pliability desiredin the final product the time of impregnation with the cold caustic bathwill vary from 1 to 30 seconds. If it is desired to give a longertreatment in the cold caustic solution the concentration of the lattermay be reduced as low as 8%, and I have found that a range of from 8 toconcentration of sodium hydroxide is satisfactory for most purposes,although still higher concentrations may be used with sheets fromcertain fibers such as cotton, rag, or wood pulp fibers that have beencooked a long time, or arti such as rayon.

The duration of the period in which pres-. sure is exerted by the coldrolls may vary from 1 to seconds, the upper limit being utilized forfibers that are not very reactive, such as slightly cooked wood fibers.The duration of the exertion of pressure on the perforated hot drum mayalso be varied, but usually corresponds to the time of pressing with thecold rolls.

The degree of pressure exerted by both the cold rolls and the hot drummay also be varied, a greater pressure being used for fibers that areonly shghtly reactive than for fibers that are very reactive."

The temperature of heating may be varied i but the best results areobtained when steam is liberated on to the sheet with a pressure of atleast 10 pounds. The best results are obtainedwhen there is a verysudden change from the highly swollen to the final swollen state. Thisis accomplished by heating the sheet as quickly as possible. While thismay be accomplished by merely passing the sheet over a heated roll, thisis too slow for optimum results, hence it is preferable to an ment theheating by injecting'steam throng the sheet.

The concentration of the hot caustic bath may be varied, using anyconcentration but the 18% concentration is.

above 15%, preferable because the quality of the product with thisconcentration is near the optimum, and because of economy in caustic.

The temperature of the hot caustic bath may be varied from 80 C. to theboiling the solution, but the best results are obtained when it is nearthe latter point, although with. certain ty es of fibers a lowertemperature'is prefera le.-to avoid appreciable degradation of thecellulose and weakening of the felt. In general I have found that thebest temperature range is from 100 to 104 C.

The time of passage through the hot caustic bath may vary from 2 .to 20seconds, al-

though the latter period causes deterioration of some types of fibers.

As an example of the increase in strength stiff and boardy.

develo ed a process of making felted celluappreciableat the line ofcrease when such papers were creased, whereas felt made by this processsuffers no decrease in strength even after repeated creasing. Likewise,sheets made from kraft fibers subjected to my process are less stifi'than kraft papers which have not been so treated and are free from thedecided paper break which is characteristic of the untreated kraftpapers.

My treatment also produces a marked increase in the wet strength ofkraft apers and felts subjected thereto, raising t e wet tensilestrength from 2% of the dry; strength to 20% or more of the dry strengtI desire to have it understood that I may use sheets or mats of anycellulose fibers, such as kraft fibers, linters, sulfite treated fibers,rope fibers, cotton fibers, including those reclaimed from tires, burlapfibers, or a, mixture of two,or more types of fibers, such as a mixtureof kraft and rope fibers or 'kraft fibers and linters. In sheets madefrom such mixed fibers the greater length of rope fibers adds strengthto the finished product and the kraft fibers give an increasedpliability. Linters that are free from very short fibers give a productof similar strengthdto long rope fibers. Fibers from wood, in general,give they be unsized.

Where high density is required more reactive fibers should be used.

Although I have referred herein to caustic solutions and have mentionedcaustic soda in particular,it will be understoodthat caustic potash orother fixed caustic alkali may be used. 1

I have found that it is desirable toheat the material while it is stillunder 'pressure to prevent the 'final product from becoming Although thepas age through the hot caustic bath can be omitted, I-have also foundthat this increases the strength of the final roduct and improves thefelting.

It will therefore be apparent that I have lose fi er roducts in whichthe fibers are held toget er in a sheet form by interlneshing, kinkingand curling of the fibers instead of by the use of binding materials,such as Y products whose 'stren h varies as the length of the fibers.

resins, glues, pyroxylin and rubber compo- Wide variety of below 5 C.

sitions; that my products are more pliable than products made by otherprocesses; and that my products have a greatly increased wet strength,and an equal or greater dry strength" than paper without being subjectto the characteristic paper break Felted cellulose fiber products'madein accordance with my invention are useful for apurposes, including abase for subjection to coating or impregnating processes with pyroxylin,rubber or other materials, as in the formation of fabrikoid orartificial leather; for impregnation in single or multiple layerthicknesses with solutions of phenolic condensation products; andwithout impregnation, as for felt hats, containers shoe counters or boxtoes.

As many apparently widely difi'erent embodiments of this invention maybe made without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended patent claims. a claim:

1. The process of making felted cellulose fiber products, whichcomprises gelatinizing continuous bands of cellulose fibers with gcaustic alkali,

subjecting these gelatinized bers to pressure and heat, and washing.

e process of making felted cellulose 2. fiber products, which comprisestreating cellul'ose fibers in sheet or mat form with caustic alkali toelatinize these fibers without dispers ng t em, pressing heatlng Whilemaintaming pressure, and washlng. The process of claim 2, in which thecaustlc alkali solution is cold.

- he process of fibers are subjected to a treatment with hot causticalkali before the washing. e process of making. felted cellulose fiberproducts, which comprises treating cellulose; fibers in sheet or matform with an 8 claim '2, in .which the menace 5 seconds to gelatinizethe fibers without dis- Eersing the cellulose, pressing the gelatinizedbers,-1ncreasing the temperature while still maintaining the pressure,move the caustic alkali.

' 10. The process of claim 9, in which the heating is facilitated by theapplication of steam under an initial pressure of at least 10 pounds.

11. The process of claim 9, in which the matis passed through an 18%solution of sodium hydroxide at 100 to 104 C. for 5 seconds prior to thewashing, to reduce the swelling of the fibers and facilitate their kinhnand curling.- I v 12. strong flexible compressed felted non-wovencellulose fiber product comprising artificially an intensely curled andk'inked fibers held to gether fibers.

13. A product comprising artificially curled and kinked cellulose fibersassociated and washing to reby gelatinization of the in a non-wovensheet form without other while gelatinized,

to 15% solution of caustic alkali to gelatinize H these fibers withoutdispersing them, pressing 'whlle gelatinized, heating pressure, and whing.

The process of claim 5;, caustic alkali is maintained at and treatmentin which the a temperature with caustic al' kali is continued. for from1 to'30 seconds.

7 The process of claim 5, in which the fibers are subjected to treatmentwith an 18% solution of hot caustic soda for from 2 to 20 seconds beforethe washing.

8. The process of claim 5, in which the caustic alkali is maintained ata temperature below 5C. and treatment with this caustic alkali iscontinued for from 1 to' 30 seconds, and in which there is a subsequenttreatment W1th a hot 18% caustic alkali solution before washing. V

9. The process of making a felted cellulose while maintaining a wettensile strength i ion

